precursor complex 

https://doi.org/10.1351/goldbook.P04806
May either indicate an encounter complex or a collision complex, but furthermore implies that this complex undergoes a reaction (e.g. electron transfer).
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2266 [Terms] [Paper]
Citation: 'precursor complex' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04806 RIS BibTex EndNote
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Last revised: February 24, 2014